US20090039802A1 - Backlight control circuit - Google Patents
Backlight control circuit Download PDFInfo
- Publication number
- US20090039802A1 US20090039802A1 US12/228,398 US22839808A US2009039802A1 US 20090039802 A1 US20090039802 A1 US 20090039802A1 US 22839808 A US22839808 A US 22839808A US 2009039802 A1 US2009039802 A1 US 2009039802A1
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- US
- United States
- Prior art keywords
- terminal
- control circuit
- pwm
- backlight control
- circuit
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Granted
Links
- 239000003990 capacitor Substances 0.000 claims description 14
- 238000010586 diagram Methods 0.000 description 4
- 230000002159 abnormal effect Effects 0.000 description 1
- 230000003247 decreasing effect Effects 0.000 description 1
- 230000007812 deficiency Effects 0.000 description 1
- 239000004973 liquid crystal related substance Substances 0.000 description 1
- 230000005855 radiation Effects 0.000 description 1
Images
Classifications
-
- H—ELECTRICITY
- H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
- H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
- H05B45/00—Circuit arrangements for operating light-emitting diodes [LED]
- H05B45/10—Controlling the intensity of the light
- H05B45/14—Controlling the intensity of the light using electrical feedback from LEDs or from LED modules
-
- H—ELECTRICITY
- H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
- H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
- H05B45/00—Circuit arrangements for operating light-emitting diodes [LED]
- H05B45/30—Driver circuits
- H05B45/32—Pulse-control circuits
- H05B45/325—Pulse-width modulation [PWM]
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02B—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO BUILDINGS, e.g. HOUSING, HOUSE APPLIANCES OR RELATED END-USER APPLICATIONS
- Y02B20/00—Energy efficient lighting technologies, e.g. halogen lamps or gas discharge lamps
- Y02B20/30—Semiconductor lamps, e.g. solid state lamps [SSL] light emitting diodes [LED] or organic LED [OLED]
Definitions
- a typical backlight control circuit 10 includes a pulse width modulation (PWM) integrated circuit (IC) 11 , a power source 12 , and a control terminal 13 .
- the PWM IC 11 includes an enable terminal 112 connected to the control terminal 13 and a power input terminal 111 connected to the power source 12 .
- the power source 12 provides an operational voltage, for example, 5 volts, to the PWM IC 11 .
- the control terminal 13 receives a control signal from a scalar IC (not shown) of an LCD.
- the backlight control circuit 10 is configured to turn a backlight (not shown) of the LCD on or off. If the LCD is turned off, the scalar IC generates a control signal having a low voltage and sends the control signal to the enable terminal 112 via the control terminal 13 . The PWM IC 11 is not operational and no pulse signal is outputted. If the LCD is turned on, the scalar IC generates the control signal having a high voltage, for example, 3.3 volts, and sends the control signal to the enable terminal 112 via the control terminal 13 . The PWM IC 11 is operational and output pulse signals are outputted to light up the backlight of the LCD.
- the operational voltage of the power source 12 can be decreased, for example, lower than 5 volts. If a high operational voltage is still provided to the PWM IC 11 , the pulse signals outputted from the PWM IC 11 is unsteady, resulting in an unsteady light emission of the backlight. Thus, a reliability of the backlight control circuit 10 is low.
- a backlight control circuit includes a PWM IC having a power input terminal, a power source capable of outputting an operation voltage, and a switching circuit connected between the power source and the PWM IC to control if the operation voltage is provided to the power input terminal.
- FIG. 2 is a diagram of a second embodiment of a backlight control circuit.
- FIG. 3 is a diagram of circuits of a third embodiment of a backlight control circuit.
- FIG. 4 is a diagram of a typical backlight control circuit in an LCD.
- a first embodiment of a backlight control circuit 20 includes a PWM IC 21 , a power source 22 , a control terminal 23 , and a switching circuit 24 connected between the power source 22 and the PWM IC 21 .
- the PWM IC 21 includes an enable terminal 212 connected to the control terminal 23 and a power input terminal 211 connected to the power source 22 via the switching circuit 24 .
- the power source 22 provides an operation voltage to the PWM IC 21 via the switching circuit 24 .
- the control terminal 23 receives a control signal from a scalar IC (not shown) of an LCD (not shown).
- the limiting circuit 36 is configured to clip the control signal and protect the PWM IC 21 .
- the limiting circuit 36 includes a second zener diode 361 , a diode 362 , a third resistor 363 , and a first capacitor 364 .
- the third resistor 363 is connected between the control terminal 23 and the enable terminal 212 .
- the enable terminal 212 is connected to the control terminal 23 via the diode 362 in a forward conduction.
- the enable terminal 212 is connected to ground via the first capacitor 364 .
- the control terminal 23 is connected to ground via the second zener diode 361 in reversed conduction.
- the first capacitor 364 is configured to eliminate an interference of the control signal and steady the control signal.
- control voltage is slightly less than the zener voltage of the second zener diode 361 , the second zener diode 361 cannot be reversely conducted.
- the control voltage is provided to the enable terminal 212 via the third resistor 363 . If the operation voltage of the power source 22 is provided to the PWM IC 21 , the PWM IC 21 is operational and pulse signals are outputted to light up the backlight.
- the second zener diode 361 is reversely conducted to maintain the control terminal 23 to the zener voltage.
- the clipped control voltage is provided to the enable terminal 212 via the third resistor 363 . If the operation voltage of the power source 22 is provided to the PWM IC 21 , the PWM IC 21 is operational and pulse signals are outputted to light up the backlight.
- the diode 362 If the control signal is changed from a high voltage to a low voltage, the diode 362 is forward conducted.
- the first capacitor 364 can quickly discharge via the diode 362 , thereby causing the enable terminal 212 to be a low voltage for stopping the PWM IC 21 .
- a third embodiment of a backlight control circuit 40 is similar to the backlight control circuit 20 of FIG. 1 , except that the backlight control circuit 40 further includes a second capacitor 43 and a third capacitor 44 , both connected between a power input terminal 211 of an PWM IC 21 and ground in parallel as shown in FIG. 3 .
- the second capacitor 43 and the third capacitor 44 are configured to eliminate the interference of the operation voltage provided by the power source 22 .
Landscapes
- Liquid Crystal Display Device Control (AREA)
Abstract
Description
- The present invention relates to backlight control circuits, and particularly, to backlight control circuits including a switching circuit.
- Liquid crystal displays (LCDs) have been widely used in various portable information products such as notebooks, personal digital assistants (PDAs), and video cameras, because of its portability, low power consumption, and low radiation. LCDs are poised to completely replace cathode ray tube monitors and televisions. A typical LCD includes an LCD panel, a backlight for illuminating the LCD panel, and a backlight control circuit for controlling the backlight.
- Referring to
FIG. 4 , a typicalbacklight control circuit 10 includes a pulse width modulation (PWM) integrated circuit (IC) 11, apower source 12, and acontrol terminal 13. The PWM IC 11 includes an enableterminal 112 connected to thecontrol terminal 13 and apower input terminal 111 connected to thepower source 12. Thepower source 12 provides an operational voltage, for example, 5 volts, to the PWM IC 11. Thecontrol terminal 13 receives a control signal from a scalar IC (not shown) of an LCD. - The
backlight control circuit 10 is configured to turn a backlight (not shown) of the LCD on or off. If the LCD is turned off, the scalar IC generates a control signal having a low voltage and sends the control signal to the enableterminal 112 via thecontrol terminal 13. The PWM IC 11 is not operational and no pulse signal is outputted. If the LCD is turned on, the scalar IC generates the control signal having a high voltage, for example, 3.3 volts, and sends the control signal to the enableterminal 112 via thecontrol terminal 13. The PWM IC 11 is operational and output pulse signals are outputted to light up the backlight of the LCD. - In some abnormal conditions, such as load shorting or overload, the operational voltage of the
power source 12 can be decreased, for example, lower than 5 volts. If a high operational voltage is still provided to the PWMIC 11, the pulse signals outputted from the PWM IC 11 is unsteady, resulting in an unsteady light emission of the backlight. Thus, a reliability of thebacklight control circuit 10 is low. - It is desired to provide a new backlight control circuit, which can overcome the above-described deficiency.
- A backlight control circuit includes a PWM IC having a power input terminal, a power source capable of outputting an operation voltage, and a switching circuit connected between the power source and the PWM IC to control if the operation voltage is provided to the power input terminal.
- Other novel features and advantages will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings.
-
FIG. 1 is a diagram of a first embodiment of a backlight control circuit. -
FIG. 2 is a diagram of a second embodiment of a backlight control circuit. -
FIG. 3 is a diagram of circuits of a third embodiment of a backlight control circuit. -
FIG. 4 is a diagram of a typical backlight control circuit in an LCD. - Many aspects of the embodiments can be better understood with reference to the following drawings. The components in the drawings are not necessarily drawn to scale, the emphasis instead being placed upon clearly illustrating the principles of the embodiments. Moreover, in the drawings, like reference numerals designate corresponding parts throughout the several views. Reference will now be made to the drawings to describe various embodiments in detail.
- Referring to
FIG. 1 , a first embodiment of abacklight control circuit 20 includes a PWM IC 21, apower source 22, acontrol terminal 23, and aswitching circuit 24 connected between thepower source 22 and the PWM IC 21. - The PWM IC 21 includes an enable
terminal 212 connected to thecontrol terminal 23 and apower input terminal 211 connected to thepower source 22 via theswitching circuit 24. Thepower source 22 provides an operation voltage to the PWMIC 21 via theswitching circuit 24. Thecontrol terminal 23 receives a control signal from a scalar IC (not shown) of an LCD (not shown). - The
switching circuit 24 includes atransistor 25, afirst resistor 241, asecond resistor 242, and afirst zener diode 243. Thetransistor 25 includes abase electrode 251 connected to thepower source 22 via thefirst resistor 241 and thefirst zener diode 243 in a forward conduction direction in series, acollector electrode 253 connected to thepower source 22 via thesecond resistor 242, and anemitter electrode 252 connected to thepower input terminal 211. - For exemplary purposes only, an operation voltage provided by the
power source 22 is 5 volts, a type of the PWM IC is OZ9910G, a resistance of thefirst resistor 241 is 1.0 kilo-ohm, and a resistance of thesecond resistor 242 is 3.3 kilo-ohm. A zener voltage of thefirst zener diode 243 is approximately equal to or larger than the operation voltage provided by thepower source 22. - The
backlight control circuit 20 is configured to turn on or turn off a backlight (not shown) of the LCD. If the LCD is turned off, the scalar IC generates the control signal having a low voltage, for example, zero volts, and sends the control signal to the enableterminal 212 via thecontrol terminal 23. The PWM IC 21 is not operational and no pulse signal are outputted to light up a backlight of the LCD. - If the LCD is turned on, the
scalar IC 21 generates the control signal having a high voltage, for example, 3.3 volts, and sends the control signal to the enableterminal 212 via thecontrol terminal 23. If the operation voltage is provided to thepower input terminal 211 via theswitching circuit 24, the PWM IC 21 is operational and output pulse signals to light up the backlight. - If the operation voltage becomes less than the zener voltage, the
first zener diode 243 cannot be reversely conducted. The operation voltage cannot be provided to thebase electrode 251 and thetransistor 25 is turned off. The PWM IC 21 will not be operational and no pulse signal is outputted. - If the operation voltage becomes larger than or equal to the zener voltage, the
first zener diode 243 is reversely conducted. The operation voltage is provided to thebase electrode 251 via the reversely conductedfirst zener diode 243 and thesecond resistor 241, thereby turning on thetransistor 25. The operation voltage is provided to thepower input terminal 211 via thefirst resistor 241 and thetransistor 25. The PWM IC 21 is operational and outputs pulse signals to light up the backlight. - The
switching circuit 24 is configured to control if the operation voltage is provided to the PWM IC 21. If the operation voltage is normal or larger than a predetermined voltage, such as the zener voltage, the operation voltage may be provided to thePWM IC 21 via theswitching circuit 24. When the operation voltage is lower than the predetermined voltage, theswitching circuit 24 disconnects thepower source 22 and thePWM IC 21 such that the operation voltage cannot be provided to thePWM IC 21. Thus, a reliability of thebacklight control circuit 20 is improved. - Referring to
FIG. 2 , a second embodiment of abacklight control circuit 30 is similar to thebacklight control circuit 20 ofFIG. 1 , except that thebacklight control circuit 30 further includes alimiting circuit 36 connected between acontrol terminal 23 and an enableterminal 212 of a PWM IC 21. - The limiting
circuit 36 is configured to clip the control signal and protect the PWM IC 21. The limitingcircuit 36 includes a second zener diode 361, adiode 362, athird resistor 363, and afirst capacitor 364. Thethird resistor 363 is connected between thecontrol terminal 23 and the enableterminal 212. The enableterminal 212 is connected to thecontrol terminal 23 via thediode 362 in a forward conduction. The enableterminal 212 is connected to ground via thefirst capacitor 364. Thecontrol terminal 23 is connected to ground via the second zener diode 361 in reversed conduction. Thefirst capacitor 364 is configured to eliminate an interference of the control signal and steady the control signal. - The control signal can be a low voltage, for example, zero volts, or a high voltage, for example, 3.3 volts. A zener voltage of the second zener diode 361, for example, would be approximately 3.3 volts.
- If an LCD employing the
backlight control circuit 30 is turned off, thescalar IC 21 generates the control signal having a low voltage, for example, zero volts, and sends the control signal to the enable terminal 212 via thecontrol terminal 23. ThePWM IC 21 is not operational and no pulse signal is outputted for lighting up the backlight. - If the LCD is turned on, the scalar IC generates the control signal having a high voltage and sends the high voltage to the
control terminal 23. - If the control voltage is slightly less than the zener voltage of the second zener diode 361, the second zener diode 361 cannot be reversely conducted. The control voltage is provided to the enable terminal 212 via the
third resistor 363. If the operation voltage of thepower source 22 is provided to thePWM IC 21, thePWM IC 21 is operational and pulse signals are outputted to light up the backlight. - If the control voltage is equal to or larger than the zener voltage of the second zener diode 361, the second zener diode 361 is reversely conducted to maintain the
control terminal 23 to the zener voltage. The clipped control voltage is provided to the enable terminal 212 via thethird resistor 363. If the operation voltage of thepower source 22 is provided to thePWM IC 21, thePWM IC 21 is operational and pulse signals are outputted to light up the backlight. - If the control signal is changed from a high voltage to a low voltage, the
diode 362 is forward conducted. Thefirst capacitor 364 can quickly discharge via thediode 362, thereby causing the enable terminal 212 to be a low voltage for stopping thePWM IC 21. - Referring to
FIG. 3 , a third embodiment of abacklight control circuit 40 is similar to thebacklight control circuit 20 ofFIG. 1 , except that thebacklight control circuit 40 further includes asecond capacitor 43 and athird capacitor 44, both connected between apower input terminal 211 of anPWM IC 21 and ground in parallel as shown inFIG. 3 . Thesecond capacitor 43 and thethird capacitor 44 are configured to eliminate the interference of the operation voltage provided by thepower source 22. - It is to be understood, however, that even though numerous characteristics and advantages of the embodiments have been set out in the foregoing description, together with details of the structures and functions of the embodiments, the disclosure is illustrative only; and that changes may be made in detail, especially in matters of arrangement of parts within the principles of the invention to the full extent indicated by the broad general meaning of the terms in which the appended claims are expressed.
Claims (19)
Applications Claiming Priority (3)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
CN20071007566.X | 2007-08-10 | ||
CN200710075663XA CN101364385B (en) | 2007-08-10 | 2007-08-10 | Backlight switch control circuit |
CN200710075663 | 2007-08-10 |
Publications (2)
Publication Number | Publication Date |
---|---|
US20090039802A1 true US20090039802A1 (en) | 2009-02-12 |
US8106605B2 US8106605B2 (en) | 2012-01-31 |
Family
ID=40390726
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
US12/228,398 Expired - Fee Related US8106605B2 (en) | 2007-08-10 | 2008-08-11 | Backlight control circuit |
Country Status (2)
Country | Link |
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US (1) | US8106605B2 (en) |
CN (1) | CN101364385B (en) |
Families Citing this family (1)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
CN109754736B (en) * | 2019-03-14 | 2022-10-25 | 惠科股份有限公司 | Detection circuit and display substrate |
Citations (5)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US4370600A (en) * | 1980-11-26 | 1983-01-25 | Honeywell Inc. | Two-wire electronic dimming ballast for fluorescent lamps |
US5909089A (en) * | 1996-04-18 | 1999-06-01 | U.S. Philips Corporation | Discharge lamp igniting and operating circuit with a timer controlled output voltage limit |
US20060245220A1 (en) * | 2002-11-29 | 2006-11-02 | Rohm Co., Ltd. | DC-AC converter and controller IC therefor |
US20060267922A1 (en) * | 2005-05-31 | 2006-11-30 | Samsung Electronics Co., Ltd. | Display apparatus with backlight driver control |
US20080068327A1 (en) * | 2006-09-15 | 2008-03-20 | Beyond Innovation Technology Co., Ltd. | Backlight module, liquid crystal display and method for controlling the same |
Family Cites Families (2)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US6570347B2 (en) | 2000-06-01 | 2003-05-27 | Everbrite, Inc. | Gas-discharge lamp having brightness control |
CN1980511B (en) * | 2005-12-01 | 2010-05-26 | 群康科技(深圳)有限公司 | Back-light open circuit protection circuit |
-
2007
- 2007-08-10 CN CN200710075663XA patent/CN101364385B/en active Active
-
2008
- 2008-08-11 US US12/228,398 patent/US8106605B2/en not_active Expired - Fee Related
Patent Citations (5)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US4370600A (en) * | 1980-11-26 | 1983-01-25 | Honeywell Inc. | Two-wire electronic dimming ballast for fluorescent lamps |
US5909089A (en) * | 1996-04-18 | 1999-06-01 | U.S. Philips Corporation | Discharge lamp igniting and operating circuit with a timer controlled output voltage limit |
US20060245220A1 (en) * | 2002-11-29 | 2006-11-02 | Rohm Co., Ltd. | DC-AC converter and controller IC therefor |
US20060267922A1 (en) * | 2005-05-31 | 2006-11-30 | Samsung Electronics Co., Ltd. | Display apparatus with backlight driver control |
US20080068327A1 (en) * | 2006-09-15 | 2008-03-20 | Beyond Innovation Technology Co., Ltd. | Backlight module, liquid crystal display and method for controlling the same |
Also Published As
Publication number | Publication date |
---|---|
US8106605B2 (en) | 2012-01-31 |
CN101364385B (en) | 2010-09-29 |
CN101364385A (en) | 2009-02-11 |
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